Thyroid Volume in Pregnancy is Associated with Parity, Gestational Age, and Body Mass Index in an Iodine-sufficient Area

O volume tireoidiano em gestantes está associado à paridade, idade gestacional e índice de massa corporal em uma área suficiente em iodo

Objective  We compared thyroid volume (TV) and presence of nodular goiter (NG) in pregnant vs. non-pregnant women in an iodine-sufficient area. We also evaluated the relationship between gestational age, parity, and TV in the pregnant women group, and determined the 2.5^th and 97.5^th percentiles of normal TV in pregnancy.

Methods  This cross-sectional study included 299 healthy women (216 pregnant) without previous thyroid diseases. Thyroid ultrasounds were performed and compared between pregnant and non-pregnant women. The range of normal distribution of TV (2.5^th and 97.5^th percentiles) in pregnancy was determined after excluding individuals with positive thyroid antibodies, NG, and/or abnormal serum thyrotropin (TSH) or free thyroxine (FT4).

Results  Thyroid volume was larger among pregnant compared to non-pregnant women (8.6 vs 6.1 cm³; p< 0.001) and was positively correlated with gestational age (rs = 0.221; p = 0.001), body mass index (BMI, rs 0.165; p = 0.002), and FT4 levels (rs 0.118 p = 0.021). Nodular goiter frequency did not differ between the two groups. There was a negative correlation between TV and TSH (rs -0.13; p = 0.014). Thyroid volume was lower among primiparous compared to multiparous patients (7.8 vs 8.9; p< 0.001) and was positively correlated with parity (rs 0.161; p = 0.016). The 2.5^th and 97.5^th percentiles of TV were 4.23 and 16.47 cm³, respectively.

Conclusion  Thyroid volume was higher in pregnant compared to non-pregnant women and was positively related to parity, BMI, and gestational age in a normal iodine status population. Pregnancy did not interfere with the development of NG.

Keywords
thyroid volume; pregnancy; iodine status; thyroid nodule; body mass index